1. Field of the Invention
The present invention relates generally to the field of wheelchairs and, more specifically, to an electrical braking system for manual wheelchairs.
2. Background Information
Numerous types of braking mechanisms for manual wheelchairs are known in the art. The most typical manual wheelchair brake is a manual xe2x80x9cover centerxe2x80x9d locking device which is activated by a lever arm and, when forced into its locking position, presses a braking member against the surface of the wheelchair tire creating a frictional braking action. Several factors mitigate against the usefulness and reliability of these types of brakes. Loss of tire pressure reduces the frictional force exerted by the crossbar on the tire and hence reduces the braking effect. A significant air pressure loss leaves these brakes useless. During transfer in and out of the chair, this type of brake allows the tire to slide underneath the crossbar and the wheelchair to move. Similarly, the brakes are ineffective and will not adequately hold the wheelchair on an incline. Other types of manual brakes include caliper type brakes manually activated with a lever arm mounted to a cable and brake assembly causing brake pads to press against the rim of the wheelchair wheel.
In these types of brakes, the frictional braking force exerted is directly related to the manual force which must be exerted on the lever arm by the brake operator to activate the brake. Wheelchair users who have arm or hand limitations may not be physically able to operate these brakes. These braking mechanisms only apply a braking force to one wheel. If an equal braking force is desired on both wheels, the user is required to use both arms and attempt to apply an equal force to both lever arms at the same time. This is difficult, if not impossible. Wheelchair frame and wheel design most often require the placement of the lever arms on the frame of the wheelchair near the user""s knees. The placement of these lever arms interferes with the user""s transfer in and out of the wheelchair. These lever arms require lifting the user""s body in order to clear the lever during transfer.
A patent to Ross and Gunther, U.S. Pat. No. 5,358,266 describes a plate attached to a braking member which applies a braking frictional force to the wheelchair tire when electronically activated by a solenoid rod. The solenoid rod is activated by means of a switch attached to the seat of the wheelchair. When the wheelchair user is raised out of the seat, the switch is activated and operates the braking mechanism. Also disclosed in this patent is a manually activated lever arm to operate the same braking member when the wheelchair user is seated. The same deficiencies discussed above apply to this wheelchair while the wheelchair user is seated. A wheelchair user with arm or hand limitations may not be able to operate the hand lever and the lever arm braking mechanism to apply a braking force to one wheel. In addition, the position of the lever arm may interfere with transfer in and out of the wheelchair.
Electric wheelchairs with various forms of braking means are common in the prior art. These braking means include gear reduction mechanisms, electromagnetic braking by means of a resistance applied to the electric motors, electronically activated frictional braking mechanisms where a solenoid is electrically energized to move brake shoes into frictional contact with a brake drum, and conventional manual brakes operated by a lever mechanism. These electric wheelchairs are heavy, cumbersome, difficult to transport and do not promote physical activity by user.
It is desirable to have a lightweight, manual wheelchair with an effective easily operable electronic braking mechanism.
It is an object of this invention to provide an electronically activated braking system for a lightweight, manual wheelchair which allows the wheelchair to maintain its lightweight and maneuverability characteristics.
It is a further object of this invention to have an electronically activated braking system for manual wheelchairs which eliminates the need for users of the wheelchair to manually operate brakes by means of a lever mechanism.
It is a further object of this invention to provide a braking system for manual wheelchairs which provides equal braking force to both wheels of a wheelchair simultaneously.
It is a further object of this invention to provide a braking means for a manual wheelchair which can be activated without the use of a manually operated lever which interferes with transfer in and out of the wheelchair by the user.
It is a further object of this invention to provide a braking means for manual wheelchairs which eliminates movement of the wheelchairs on inclines and during transfer in and out of the wheelchair by the user.
It is a further objection of this invention to provide a braking means for manual wheelchairs which allows for detaching the wheelchair wheels without disturbing the braking means.
In order to achieve these objectives, this invention provides for an electronic braking system, which is comprised of a braking means, a cable pulley system for activating the braking means, a DC liner actuator with actuator rod connected to the cable pulley system, a motion limit switch, a rechargeable twelve-volt battery electronically connected to the DC actuator, and a double throw control switch electronically connected to the battery for activating the battery power.
It is anticipated that the preferred braking means is a caliper-type brake positioned to clamp onto a metal disk mounted axially to a hub which rotates on the axil of each wheelchair wheel. The hub on which the disk is mounted mates in gear fashion with the hub on the wheelchair wheel. The mating hubs are locked together with a locking pin which extends axially through the center of the mated hubs such that the hubs are locked and rotate together when the wheelchair wheel is turned.
The braking means for each wheel are connected to opposite ends of a cable wire. The cable wire passes around a pulley such that displacement of the pulley provides equal force and displacement to said opposite ends of the cable wire. The ends of the cable wire are directed through small openings in a mounting bracket. The openings are spaced a distance equal to the diameter of the pulley so the cable wire remains parallel as it extends from the pulley through said openings. A circular pulley cap is placed concentrically over the pulley. The vertical side of the pulley cap has two openings to allow for the passage of the wire cable into the pulley cap through the first opening, around the pulley and out the second opening. The pulley cap, pulley, and cable wire assembly is then connected to the outer end of the actuator rod by a coupling bracket.
The DC linear actuator is mounted on the wheelchair in a manner to allow the actuator rod to extend and displace the pulley and cable wire in line with the actuator rod""s axis. The DC linear actuator is electronically powered by a twelve-volt rechargeable battery mounted to the wheelchair. The battery power is activated by a double throw control switch mounted to the wheelchair in a position where it is easily accessed by both the wheelchair user and a person assisting the wheelchair user.
The double throw toggle switch can be thrown in two different directions. When the double throw toggle switch is thrown in the first direction, it will cause the actuator rod to retract, pulling the pulley and cable wires and activating the braking force. When the toggle switch is thrown in the second direction, it will cause the actuator rod to extend, pushing the pulley and cable wire and deactivating the braking force.
In order to limit the tension in the cable wire, a motion limit switch can be added to the electrical brake system. The motion limit switch is wired into the circuit between the double throw toggle switch and said DC linear actuator. The motion limit switch is activated by displacement of the actuator rod in the direction which pulls the cable wire and activates the braking means. Once a selected braking force is attained, the motion limit switch opens the circuit and stops the displacement of the actuator rod.